The UN nuclear watchdog said in a report released Saturday that Iran had complied with its obligations under a nuclear deal reached with six world powers in July, paving the way for the lifting of sanctions.

"Iran has carried out all measures required under the [July deal] to enable Implementation Day to occur," the Vienna-based International Atomic Energy Agency (IAEA) said in a statement.

Certification by the IAEA will allow Iran immediately to recoup some $100 billion in assets frozen overseas. Tehran will also see huge benefits from new oil, trade and financial opportunities after the international sanctions against it are lifted.

In a statement delivered in Vienna Saturday evening, IAEA Director General Yukiya Amano said it was "an important day for the international community" and noted that the green light given by the UN agency meant "relations between Iran and the IAEA now enter a new phase".

US lifts sanctions

Shortly after the IAEA announcement, US Secretary of State John Kerry signed documents confirming that the US government had received the report and waivers to implement the lifting of US Congressional sanctions.

"I hereby confirm that the International Atomic Energy Agency has verified that Iran has fully implemented its required commitments ... The US sanctions-related commitments ... are now in effect," Kerry said.

Separately, in Washington, US President Barack Obama signed an order revoking previous executive orders imposing further sanctions beyond the scope of the Congressional sanctions.

At a joint press briefing with Iranian Foreign Minister Mohammad Javad Zarif on Saturday, EU foreign policy chief Federica Mogherini said the nuclear deal was now in force.

The EU procedure for lifting sanctions should be rapid. An official decision of the European Council, which brings together the leaders of the 28 EU members, is required to finalise the process.

US, Iran reach prisoner-swap deal

Progress also came Saturday in another area of Iran-US tensions: US and Iranian officials announced that Iran was releasing four detained Iranian-Americans in exchange for seven Iranians held in the United States.

US officials said the four Americans – Washington Post reporter Jason Rezaian, former US Marine Amir Hekmati, pastor Saeed Abedini and Nosratollah Khosravi-Roodsari – were to be flown from Iran to Switzerland on a Swiss plane and then brought to a US military hospital in Landstuhl, Germany, for medical treatment.

In return, the US will either pardon or drop charges against seven Iranians – six of whom are dual nationals – who are accused or convicted of violating US sanctions. The US will also drop Interpol "red notices", essentially arrest warrants, on a handful of Iranian fugitives it has sought.

Rezaian is a dual Iran-US citizen convicted of espionage by Iran in a closed-door trial in 2015. The Washington Post and the US government have denied the charges, as has Rezaian.

The landmark Iran nuclear agreement, struck on July 14 after decades of hostility, defused the likelihood of either US or Israeli military action against Iran, a threat to which Zarif alluded.

"Our region has been freed from [the] shadow of an unnecessary conflict that could have caused concerns for the region," he said. "Today is also a good day for the world. Today will prove that we can solve important problems through diplomacy."

Iran has long insisted that all of its nuclear activities are peaceful. But under the July 14 deal, it agreed to roll back nuclear programmes that could be used to make weapons in return for an end to sanctions. The agreement places Iran's various nuclear activities under IAEA scrutiny for up to 15 years and includes the option of re-imposing sanctions should Tehran break its commitments.